The measurement of acoustic vibrations in a well can be used for localizing a source of noise, and in particular, such a technique can be used in relief well to locate a well that is blowing out. The relief well must be drilled towards the well that is blowing out, which means that it is necessary to determine the direction thereto by means of a device located in the relief well. The technique described in the documents mentioned below relies on the phenomenon of sound waves being generated by a well that is blowing out.
The apparatus described in U.S. Pat. No. 4,703,459 comprises two cylindrical transducers mounted in opposite directions and disposed at a given distance from each other. At the depth where a measurement is to be taken, the apparatus is turned through 360.degree., and the signals from the two transducers are processed in order to determine the direction of the source of noise. This technique is not sufficiently accurate.
The technique described in European patent applications No. 0 138 271 (corresponding to U.S. Pat. No. 4,711,303) and No. 0 224 285 consists in measuring acoustic vibrations at a given depth in a well at a plurality of points distributed angularly around the axis of the well, with the measurements being performed by a triaxial set of accelerometers placed against the wall of the well or at a short distance therefrom. The accelerometers are disposed at the ends of arms hinged relative to a body which is centered in the well, with the system of arms being rotatable about the well axis.
After each measurement, the system of arms is retracted in order to withdraw the accelerometers from the wall and then turned through a given angle, e.g. 10.degree., prior to being redeployed to bring the accelerometers back into contact with the wall or to bring spacer members mounted at the ends of the arms into contact with the wall, after which a further measurement is taken.
The time necessary for acquiring all of the measurement points at each given depth, e.g. 36 points in the above example, is extremely long: about two hours. This is an excessive amount of time in a situation where the target well is continuously blowing out fluids which are harmful or dangerous.